Capsule-making machines have been developed to utilize dip-molding technology. Such technology involves the dipping of capsule-shaped pins into a gelatin solution, removing the pins from the solution, drying the gelatin on the pins, stripping off the gelatin capsule parts from the pins, adjusting for length, cutting, joining and ejecting the capsules. Prior art capsule-making machines have utilized a combination of mechanical and pneumatic elements to perform these functions in a dip-molding technique. While these apparatus are, in general, suitable for the intended purpose, it is desirable to produce capsules by injection molding them while at the same time precisely controlling the properties of the gelatin in order to produce the capsules hygienically and with minimum dimensional deviations so that the capsules can be filled on the high speed equipment.
A prerequisite for any material to be moldable by an injection process is its ability to pass a glass transition point at a temperature compatible with the thermal stability of the material and the technical possibilities of an injection molding device. A further prerequisite to the use of any material for delivering shaped products of high dimensional stability in an injection molding process is a high minimum elastic recovery after the mold is opened. This parameter can be adjusted by manipulating the dispersity of the material at the molecular level during the injection process.
The following patents describe suitable compounds or mixtures which may be injection molded into various articles.
Shirai et al. in U.S. Pat. No. 4,216,240, describes an injection molding process which produces an oriented fibrous protein product. To obtain a flowable mass for the molding process, the protein mixtures used by Shirai et al. have to be denatured and thus lose their capacity to undergo dissolution.
Nakatsuka et al., in U.S. Pat. No. 4,076,846 uses binary mixtures of starch with salts of protein materials to obtain an edible, shaped article by an injection molding process.
Heusdens et al., in U.S. Pat. No. 3,911,159, discloses the formation of filamentous protein structures which produce edible products.
In addition, the method for determination of the molecular mass distribution of the various types of gelatin used in the present invention is described in the following references:
I. Tomka, Chimia. 30, 534-540 (1976)
I. Tomka, et al., Phot. Sci. 23, 97 (1975)
The use of an injection molding device for producing capsules of gelatin and other moldable hydrophilic polymers with similar properties, however, is new and has not been suggested in the technical literature.